Learn Dutch: Er zit bloed op mijn hand. - There is blood on my hand.

English uses 'there is' for almost everything, but Dutch prefers verbs of position (zitten, staan, liggen). For things that are attached to a surface, stuck on something, or located inside a container (like dirt on a shirt, a stain on a wall, or blood on a hand), Dutch uses zitten.

What is the function of Er at the start of this sentence?

Er acts as a dummy subject here, just like 'There' in 'There is blood.' In Dutch, when you introduce a new, undefined subject (like bloed without a specific word like 'het' or 'mijn' in front of it), you typically start the sentence with Er and place the actual subject later in the sentence.

How would I add the explanatory word namelijk to this sentence if I wanted to explain why I need a bandage?

You would place it right after the conjugated verb, making it: Er zit namelijk bloed op mijn hand. (There is blood on my hand, you see). In sentences starting with the dummy subject Er, the adverb namelijk goes into the middle field before the actual undefined subject (bloed).

Why is it mijn hand and not plural if I have two hands?